There wasn't a whole lot of point to upgrading this thing, since no matter what, all you has was an original ISA bus. I did swap the 8088 for a NEC V20 which was a noticeable update, and I added an 8087 math coprocessor - one of the few thing I had that took advantage of it is this Star Trek game called Begin, where you issued commands for a fleet of ships and attacked a fleet of whichever enemy you picked. Lots and lots of angle calculations as some of the larger ship types could launch a LOT of torpedos - and each torpedo could be independently targeted! If you picked the maximum size fleets for both sides, it crawled - but with the 8087 it was incredible. Of course run it in a DOS window on a modern machine and you wonder why it would be so slow back then.
There was for a time a company that made 80286 upgrades for 8088 PCs - the card plugged in to a slot and connected to the 8088 socked with a 40 pin ribbon cable. As you might expect - it failed horribly. Very unreliable, and prone to lockups - and that's AFTER I added a grounded shield to the ribbon cable. And it didn't give true AT performance anyway - you still used the 8 bit memory and ISA bus.