I've noticed when Tixati is allocating large files (10+GB) the GUI gets very laggy, sometimes not registering a click for a whole second and occasionally saying "Not Responding". Scrolling down a list will result in "artifacts". IT looks like entries on the list pile up or cut each other off when scrolling up or down. Thit does not go away until you stop scrolling. The severity increases with heavier disk usage.

Please note that Tixati is installed on my C drive, an SSD. And is set to download only to my D drive, an old 500GB HDD (66MB/s Read & 65MB/s write).

I have the same issue, just wait till the last file has finished allocating/initialising before adding the next.

I also had that issue then my out drive failed. It might be that is where yours is headed.

i have the same issue - win 7 pro 32 bit, ssd.

the problem was there when it was downloading to the ssd and as it is now - downloading to a nas device.

Same issue, sadly not only during allocatino, also at startup while scanning. Also quick clicks (browsing) thru the torrent trasfer list times out the GUI for a bit.
Btw.. is it possible to disable the scanning at startup. Dunno why it scans the same files everytime i startup. Really annonying.

You don't want to saturate the disk bus. Try to seed from a different physical disk than downloading. Move/relocate in the background.
As far as SSD I have heard using a RAMdisk helps with bottlenecks

Uncheck the "auto check at startup" in Settings.
In Settings -> Files you can try CHECK "skip last write time check" for both unreliable drive, and NAS...