I've been a .30-06 fan for years, but I have to admit I'm really intrigued by this resurgence of the .35 Whelen. I'd be in agony over which one to choose if I was in the market right now. I'll just keep telling myself over and over and over that I don't need one. Maybe that'll work.
As for reliability, I own two 7400's and a 742, and my father and 4 uncles all hunt with 7400's, and we've never had any reliability issues with them.
I hate saying things like "you really have to keep them clean" on forums like this, because that statement carries the implication that anyone who has had problems with their firearm is obviously a brain-dead irresponsible cretin who shouldn't be allowed to mangle anything more advanced than a slingshot - but I have to say it anyway... The only time I've ever known one of us to have a reliability issue with a 7400 was when we let it get really nasty before cleaning it out.
Having said that, Remington claims the 750 is more reliable, but since the investment of a large amount of capital is involved on their part, you may want to accept that as a claim and not an established fact for the time being.