Thinking about purchasing a new stem to help sort out problem I get in the lower part of my back. Currently got a stem with a 5 degree rise. Will I notice an increase in 1 degree with a new 6 degree stem?

It moves the bar by less than 2mm on a c. 100mm stem.

Personally i would notice it but I would soon (as in 10 minutes) get used to it.

Might be worth getting a cheaper stem with more rise, just to see how it feels before buying an expensive replacement that might not make any difference. You can always keep the cheap stem I think it’s good to have a selection of inexpensive kit to experiment with.

Will I notice an increase in 1 degree with a new 6 degree stem?

only if you write reviews for magazines 😉

No. You won’t notice it. Not ever.

OK cool, might go down the route of some new bars then with a higher rise than my current ones which are 1.5″

with a 100mm stem the difference is 1mm less reach and 2mm higher

with a 80mm stem the difference is 1mm less reach and 1mm higher

with a 60mm stem the difference is same reach and 1mm higher

[assuming a 70 deg head angle]

see http://alex.phred.org/stemchart/Default.aspx

Personally i would notice it but I would soon (as in 10 minutes) get used to it.

No you wouldn’t! If no one told you? Your bars flex more than that!

Only if you would notice that your saddle is 2mm lower than usual!