To cut a very long story short, I am in the process of buying / building a short travel XC bike, and am leaning heavily toward the top fuel 8 or 9 which i have ridden and really like. I have accumulated enough finishing kit, gruopset and carbon loveliness (which are all fairly new and are on my current hardtail) to immediately upgrade the new bike to a really nice spec, based on that, common sense sense tells me to buy the top fuel 8 which has the exact same frame as the 9 and put all the nice bits on that. The only 2 things that would be different then between the 8 and the 9 if I did that would be a RP2 shock instead of an RP23, and a REBA fork instead of a SID. Now having ridden both REBA and SID, I reckon I could live without the SID and the REBA would be fine, but I dont know what the bike would lose in terms of handling and performance with a RP2 over an RP23 ? Anyone got an opinion on that ?

I've got a Top Fuel with an RP23 and ride with it on the most 'locked' setting the vast majority of the time, I'd happily have an RP2 and just set the bike up accordingly. If you like to fiddle with adjusters then the 9 is probably the better bike to have.

Good choice of bike by the way, love mine!

RP2 is fine two setting instead of one Who needs the third (Two setting are propedal on/off)

Actually the RP23 just has 3-levels of setting within the 'locked' position, so it's 4 positions, still not that useful!

Yes, rode my mates TF9 and it knocks spots off my hardtail on the bumpy flat sections. Most of the kit I have to put on the bike would make it top spec, but wouldnt want to get to the stage that I'd be selling myself short on the shock and forks.
My initial thoughts that it wouldnt make any difference to me but if I felt that I'd sold myself short on the important stuff by saving a few quid I'd regret it. And I am definately not an on the fly lever twiddler. I am a set and forget man

Anyone any opinions on 100mm REBA over 100mm SID ? Love the Reba I ride now, but is it loads heavier ?

Not loads no, but it is heavier.

RP2 is usually an OEM shock supplied by the bike manufacturer and is tuned for the bike. The RP23 is retail and comes with the three settings for a 'one fits all'. I beleive.