On my laptop (Acer Aspire 6530G with AMD Turion X2 Dual Core 2.0 GHz, ATI Mobility Radeon HD 3650 512 MB VRAM) and Windows 7 I'm getting between 310 and 320 FPS when idle and between 280 and 290 FPS if I do lots of mouse movments which cause selection sprite to move to other tiles.
The performance isn't affected by the size of the map so you did it.

BTW you can use any visual component as Aspyhre renderning target. So you don't actually need to create a new form for renderning area but simply use TPanel component for instance. Offcourse having dedicated form is advised if you are making FullScreen mode game to gain aditional performance.
The reason why I'm telling you this is becouse currently when I launch your program both form sizes exceed the size of my screen so I can't see whole program of yours.