I ran an Isis with the same fork for about a year. I loved it! I did run with a Reba for a while (115mm) and it put the bike in a great XC type position. The Marathon slackened the HA a bit which I prefer.
I'm not sure what the HA of the Joker XC was (nor am I really clear on how this bike differed from the Isis - thicker tubeset maybe?). I'm assuming 70 degrees? Any 100mm - 120mm fork will work. Marzocchi tends to have longer axel to crown lengths than say, Fox or Rock Shox. So, for example, a RS Revelation set at 120mm will be shorter than a Marathon at 120mm (probably) so you'd get the steeper HA w/o losing any front wheel travel. I think this would be a minor, but significant difference.
If you're on a budget check out the RS Recon. Or buy used. A nice Talas fork would give you the option to play with the travel settings. Plus, you could get a Fox fork modified for your riding style by sending it to Push Industries. It would also rejuvenate any used fork you buy.
Bottom line, get something with travel adjust and you can hunt for that sweet spot.
www.pushindustries.com
