The lowest write speed of the crucial M4 (175MB/sec) is still much faster than even an 10K RPM HDD, not to mention - the SSD can keep up the maximum write speed (up to a point) whereas a HDD cannot.
Unless you are doing video editing/RAW image file transfer's all the time - you don't need much write speed for SSD's. The main thing about SSD's is their very low latency read speed.
Do you have any other drives that can write at 175MB/Sec? If not...you shouldn't worry about the "low" write speed.
I'm using the M4 currently - and I don't notice the "low" write speed. All of my other drives cannot even reach the write speed of my SSD. The closest that my drives get to that speed is my 64GB USB key which can R/W about 120MB/S.
My computer boots up in about 15~ seconds, that's to desktop - and ready to launch any programs.
I own two Crucial M4 (64GB boot drive and 256GB games drive).
But with only 124GB of space I'm guessing you want this as a boot drive with enough space for a few program's (Office, anti viruse etc) if this is the case then the write speed won't make any difference because once you install the data your not going to be putting more and more on the drive. It's the read speeds that make the biggest differences on SSD.