Which Clipless pedals?

Looking for pedal/shoe combo that will be suitable for both my road bike and fixed hhsb (will definitely keep cages and straps on my beater).

Research today has taught/shown me:

Time ATAC - best all round system for madskidz and longer rides
Look Keo / SPD-SL - best long distance road pedals, not good for madskidz
Eggbeaters / SPD - good for mtb, create hotsposts on feet and tiring on longer distances (unless used on a platform pedal)

Does this sound fair?

I have no intent on currently buying more than one shoe/pedal combo, so want to get this right. For that reason I want to use MTB shoes. Also, I don't have the bills to shell out on £180 SIDIs so is the ATAC system compatible with Shimano shoes such as the XC50 as both use 2 bolt cleats?

is there any difference when out of the saddle and pushing hard? (smaller contact area) ?

I'd go with some platformed SPDs. Best of both worlds. The magazines will tell you that you dont get the power transfer compared to proper road pedals. But they are talking about tiny differences.

I like the crank bros system. But I would'nt go for eggbeaters fixed.

I have Crank bros Quattros on my fixed, with some carbon soled road shoes, with 3 bolt Quattro cleats. More often then not though. I just use my MTB shoes with Candy cleats. The difference is pretty minimal TBH.