My game is still in early phase of development
. Also I don't need Alpha, as my game will use custom graphic format tailored to way game works (kinda like NES' CHR files). So I need to go as low level as possible, but not too much low-level. That's why I want to use TImage - I can easily save screenshots and don't need to do a thing in OnPaint event - if another window moves over my game's, screen won't "disappear".
Also, maybe I wasn't clear enough. That's ok.
The flickering I'm afraid of is due to constantly resizing TImage as in my code sample, not speed of drawing operations.
I'm afraid of something like this (epilepsy warning):
http://imgur.com/ke1NmNB - not actual in-game graphics.
//edit: Also if I decide to release sources of my game, you probably won't learn anything from it. My code is terrible and even I barely understand it. But hey, it works!