Booting is predominantly a read-task. In fact, I think it's just a read task...
So no, the relatively low write performance shall not hinder your boot times.
Ignore the write times on the M4s. That is maximum write speeds while using 1024k data rates. Windows only uses between 4K and 8K, at which, the M4 is one of the fastest drives around. The sandforce controllers brag 500mbps write speeds, when in actual windows tasks they perform slower than the M4.
You can use WinBootInfo to view any i/o during boot, I would imagine that it would only be the odd logs that would be written to the drive during boot.
Op. that msata drive will operate at sata2 speeds due to a limitation of your motherboard. Not that that will make a difference during boot.
Do disk cleanup - You probably have installation files and service pack backup files still installed. Disk cleanup, then view system files to clear them all.
Also, disable hibernation saves like 10gb I think