I think you will not regret your choice.
As for the 750HD 5400rpm – I have in my MBP also a 5400 disc and it’s just fine.
The extra internal capacity can become handy, if you are a lot on the road and if you have big banks – presets, foley libraries or so, which you wanna store in the machine.
Also the 5400rpm is getting less fast hot, than the 7200rpm.
It’s give and take. I personally would be fine with 500GB and go for the faster one.
And the RAM is really cheap – check OWC (other World Computing) – you get damn good RAM there – a lot cheaper than with Apple.
GOOD LUCK with your new machine!!!!
Sascha