How much faster will I be on an Aero road bike compared to my Gravel bike

Thanks for some great comments, also some cynical people on here, I am not bragging I only gave the information to enable sensible reply’s which the majority are, Because I also care about how the bike looks to some on here seems wrong.
Little insight into me.
51 years young, racing mountain bikes since 1987. Organised races for NEMBA, UCI commissaire for a few years.
Ride totally solo due to the job I have. Strava has given me a new zest for riding. Ride/train 5000 miles a year. was due to do the dirty Reiver this weekend.
Can’t ride MTB’s anymore due to my job and the risk.

Out of curiosity @Zap what Aero bike are you thinking of?
Other facts when contemplating an Aero Bike, or indeed any bike:
N+1.
A pretty bike is a fast bike.
A pretty bike is a regularly used bike.

The 90’s called, they want their physics-fail back.

Fair enough TINAS, was that wind tunnel testing just based on the listed stock bikes? If so what what was the basis for the Reference “Classic Road Bike”?
Is it a theoretical average based on the same testing being applied to a several non-aero bikes or just a single bike chucked in for reference in which case why isn’t it named? As much as Aero machines vary in their drag coefficient I’m sure non-aero bikes can, surely that warrants proper examination in itself?
TBH I’d be more interested to see them examine the the Aero effects of different wheel profiles in isolation from the frame/forks?

I mean there’s a lovely spread of aero bikes there but only one generic reference point to benchmark a non-aero equivalent, seems a little “opaque” as comparative data.

It’s fine to rubbish the idea of efficiency or weight saving for climbing, I’ll accept weight saving isn’t the be all end all, but any extra Watts expended climbing inevitably dent a rider’s output latter in their ride, including on the flat, We’re not talking about TTing here, more general road riding up and down as well as along the flat…

My original point was really that for a relatively modest spend (compared to an Aeroad bike) The OP could probably pick up a reasonable (rim braked?) non-aero road bike with better rolling 25mm tyres and maybe a bit of minor aerodynamic benefit that would probably save a significant chunk of mass over his 47mm tyred, more robustly built gravel bike, and still probably slip through the air marginally more efficiently, thus skimming a bit off his average speed by default…

Throwing money at the aero arms race is really a game for Time Trialers, the benefits for more “general” road riders are increasingly marginal (vs cost), beyond maybe investing in a deeper section front rim…
How much more is a “normal” road rider really going to benefit from chucking ~£4k+ at a System Six?

Just been out on my aero bike now. The good thing with mine is that it’s lighter than a lot of “normal” bikes. Has 1580gram 50mm wheels on it, climbs well, but it’s so stable at 25/30mph. It’s such a fun bike to ride. I’ve just completed a short 22 mile ride, not much climbing but rolling hills, it was immense fun.
I have other road bikes, but none of them come close to the Aeroad in performance terms.
I have a slight downhill section near mine, for 5 miles it’s great fun smashing that as hard as possible. Yes it’s also possible on a normal bike, but it’s not the same.

Cookeaa – I completely agree that an Aero bike is in the smaller gains over tyres on the existing bike. But if the OP wants a new bike and is going to buy one for £4K, then why not an aero bike?
I do think you are looking at closer to £5k for something decent though. It’s then a question of whether it’s worth spending that.
I also have deep wheels on a normal carbon bike, but it’s disc brake. It rolls on the flats reasonably well, but for climbing it really feels like it stalls. Whereas the lighter aero bike (rim brakes) climbs really well.
Just looking at a small segment near me, 0.6 miles and 2.3 hill, I’ve gone up it 37 times but I can tell by looking at the times when I’ve done it on the Aero bike and when on a different bike.
I’m not a TTer but I did used to road race and was training to race again this season after two seasons out.

The top 20 fastest road bikes in the world, according to Strava

Aero bikes make the top 3…

2mph I recon, and you’ll feel like you are riding a jack hammer bare back compared to your current set up. On a smooth road though you’ll love it.

Not sure why people think modern aero bikes are uncomfortable. I’ve got an Aeroad, had a Madone and hired a Systemsix and test rode a Venge for a week. I honestly wouldn’t say they are uncomfortable or jarring on bumpy roads. Yes they’re not an endurance bike, but I find them fine. (I’m someone with neck injuries from my rugby league days and have limited grip or use of my left arm, I have no problems with an aero bike on bumpy roads, I get no more neck and shoulder pain after 80 miles on the aero bike than I do on my Domane with the front and rear isospeed and 32mm tyres)