How much power do I need for my power amp?

[haddimudd]

Don't worry, I didn't plan to put everything together in one rack. Yet, when adding up everything to be carried to the next gig location, I don't mind the lesser weight of some components. I used to carry a 45kg (~90 lbs?) 4x10 cab up and down stairs without help, it worked, but now I rather prefer a more lightweight oriented gear, especially if it gives me the same quality.

[geddy]

Looking around at these I'm getting the idea these are some of the best deals given the listed specs. One place has an rmx850 for 299.00 new (399 for the rmx1450), two of those bridged mono would fit my needs perfectly. For that price it seems too good.
 
I'll be running one of them each into a schroeder 410 and one into a 2x12 schroeder or 2x15 peavey.
Do you guys think two rmx850's would give me enough headroom or would the 1450's be more suitable?