Etcman: Yeah, the MTK is pretty slow since it's using A7 cores. In this case, the whole quad-core aspect is just pretty much only used for marketing. 4 slow cores = still a slow phone in most cases because a good fraction of apps are not written for threaded performance as they are targeted at low-mid range smartphones with a faster single core processor.
Not entirely sure how easy it would be to port an existing popular ROM to your specified device but that would require you to obtain drivers for the hardware to insert into the ROM. If you are planning to just mod and repackage the stock ROM that the device comes with, should be easy enough but a lot of the cooler mods out there would require code changes to the kernel and OS itself.
Overall, sounds like a bit of a hassle in the case of modding but that is up to you if your budget is of a hard limit.
Budget is less of an issue than my ability to justify the purchase amount. My wife has said multiple times to stop p1551ng around and get whatever I want. (She is using that as an excuse to allow her to buy diamonds I suspect)
But as I have no need of data based services and will only use them at work or home ~$900 (depending on HTC or S4) is a little disproportionate.
I have a buddy that has an S3 he replaced with an HTC that I can get for ~$300 so that may be the way forward but I am enjoying the knowledge upskill both in terms of a non windows based OS and of course all the shiny shiny hardware...
Ultimately however, it is the modding (hassle) that I find most attractive so whatever choice I make, I would like it to be the most feature rich option to make thepossibilities of what I can do wider.
I had a 80% functional Android OS on the iPhone 3Gs with IOS as a dual boot(Could never get push email from work flowing correctly and a couple of other things) and if I could get a fast enough processor to handle alternate OS's on the handset I choose through emulation or whatever I would be even happier.
Anyway
I am enjoying this process more and more!