I have decided to go for a 5.25 component system for my front doors.
How deep can they be to fit in our doors?
I'm choosing between:
JBL GTO 506c
Rockford FNP2514
MDS DL5 comp

Any other suggestion in the same pricerange?

almost any 5.25 set will fit. You'd have to find something pretty strange to find one that wouldn't fit.

In that price range other models to look at:

MB Quart DSD-213
Alpine SPR-136A


Personally I would go with the Quart's for that price range... but it all depends on what sounds good to your ear.

I have tried every 5.25 over the past 20 years just for you Yes they all fit.