i think i well tuned, 1800cc BGT could get you on par with a mildly tuned 914. a stock 1800cc MG engine is good for anywhere from 90-100 HP. if you threw in a Miata 140 HP engine and a 5 speed, you'd be ripping 914-4s all day long. now, a 914-6 might be a different story.
{{ to be honest, when i first started looking for a project car, i was going to buy a 914-4 for $300. it wasn't running and i didnt know much about them. the car was soon sold, and i was looking at a 1972 VW Karmann-Ghia (often called the poor man's Porsche Speedster in the late 60's). search made a sudden turn into MGs. }}
but to repair, build up, buy parts, etc... an MG will be much cheaper than a Porsche and slightly more expensive than a VW. i mean, a rebuilt, complete, warrantied MGB 4 speed tranny with overdrive will run you $1500. the same thing for a 914 would be about $3000 or maybe more.
i have found my B very simple to work with, and if you're scared of ruining it (like i am), parts cars are easy to find and just as easy to dissassemble. my parts car is a complete 1977 convertible which is just beyond help. but i have already learned how to take the rear end apart and how the gas tank system works. (cost for the parts car: $10). try finding a $10 parts car for a 914, and you'll be searching for along time.
i still like the 914s and i would consider one for my next project, but i really like these little british cars. having driven in a fully restored 1972 convertible with a well tuned weber downdraft carb and a documented engine, i know that you can sqeak the tires in second with ease.
now....if you want to talk about cheap rebuilds with some additional value AND british power, you're looking at a Triumph TR6, IMO.