Finding good V6 heads is challenge number one. Both of mine were cracked on a 77K mile car. The 2.3 with a good tune & free flowing exhaust has comparable HP numbers to a V6, is a bit lighter, gets slightly better fuel mileage & is waaaaay easier to find parts for.
A good running V6 has a smoother idle & a little better pick up from a standing start. Pinto V6 was automatic only but I know people used MII V6 4-speeds to go stick. I'm sure some T5's made the swap too but I've never researched the swap.
A V8 gets 10 mpg, mine sure did, but with patience & a good combo of parts you could see 20 mpg out of it. EFI/T5 swap maybe 25 if you drive normally. Engine mounts are expensive, frame mounts either need welded or holes drilled. Oil pan & pickup are expensive as are MII manifolds & most headers. Most run hot if you don't spring for a good radiator. The rear axle needs swapped to an 8" at the very least. Auto trans kickdown is a bear to fit just like the dipstick tube so get Lokar parts to make it easy.
A 2.3T swap is as cheap as it gets if you find a complete parts car (Merkur, Turbo Coupe or SVO) that runs. Several Merkur's have been on craigs under $600 but you have to be ready to pounce on them. I've been rounding up turbo parts off craigs for over 2 years as cheap stuff pops up. A total cash outlay of roughly $2500 over that time has netted me 4 complete shortblocks, several good heads (hard to find crack free), VAM's, intakes, 2 IHI & 2 T3 turbos, several E6 manifolds, intercoolers, a Merkur engine harness, several T5 trannies, 2 D5, 2 D9 & 2 bellcrank bellhousings plus boxes of other parts. A good low mileage 302/C4 with all the parts needed to install it in a Pinto can cost 2/3 of that.
You will need a Pinto 2.3 oil pan & pickup & a high pressure external fuel pump but the rest can come right from the parts car with little other expense. If you go auto the C4 is your best bet but the bellhousing can get pricey. The T5 swap is easier & cheaper if you like stick.