I have a T410s and use an mSATA with the screw on adapter. The clean look version.
http://www.ebay.com/itm/Mini-PCIe-PCI-e ... 418646d02e
I have 8GB of ram with a 128gb mSATA SSD. I have several 320gb drives sitting around that I have been planning on using as secondary drives. I have acquired quite of few Thinkpads over the last couple of weeks. My most recent purchase (last night) was a
2522-4BU T410 i5-520M(2.4GHz), 2GB RAM, 320GB 7200rpm HD, 14.1in 1440x900 LCD, 256MB nVIDIA Quadro NVS3100m, CDRW/DVDRW, Intel 802.11agn, Bluetooth, Modem, 1Gb Ethernet, UltraNav, Secure Chip, Fingerprint reader, Camera, 6c Li-Ion, Win7 Pro 32
My total is now three T410s and three T410 models. I have sold two of the T410 series to people which brings my total back to four. I ordered a couple SSD drives to try out in the T410 model. I am testing the bus speed of SATA II, Trying to determine if there is a bottleneck on speed. This will influence my purchasing decisions.
With the some of the 120-1280GB drives they dial back the performance by using lesser quality parts (eg. controllers) than the 240GB and up models. I have a couple of Toshiba drives in my custom built PC. I plan on pulling one out that is linear in both read and write speed to test in one of the T410 models.
My advice is to stick with what you have in your T400 in the CPU. You already have 8GB of ram. I always advise people to stick with a 128GB SSD for their main drive and use a HDD in the ultra bay for backup memory on older Thinkpad models.
I always plan ahead. I will eventually get T420s models and I have been buying 7mm SSD drives for future upgrades. I also advise people who like to tinker or build/rebuild computers to buy interchangeable parts for future computers and upgrades.

T43p,T61,X200,X200s,x201,T500,W500,T510,T410,T410s,T420s,T430,T430s
