All good advice so far but here is a thing or two to consider when making your choice between the XS and the Explorer II.
1. The latest software version on the XS series was a tad bit faster than the original XS but hardly notable unless you owned both at the same time. The real differences made to the later version concerned the cam lock issue and a few software revisions enhancing stability.
2. When the Explorer II was released, there was quite a few of the first batch shipped that had SEVERE stability issues. Ask me how I know

. Minelab did address these issues pronto .... BUT ... even if you buy a new EX II that came off the assembly line today it WILL BE more susceptible to electrical (RF) interference than the XS series !
For those that have followed the progress of the Explorer since they were released and traded up along the improved technology highway can attest to this as FACT. Simply put, the latest XS series is more stable than the EX II when subjected to RF interference.
For those that have both and might DOUBT this, try a little experiment and see for yourself.
Example> I can turn on my HDTV in my living room that faces the front of my house, go outside and turn on my EX II and it will not stabilize until I back away at least 40 feet in-line with the HDTV. The XS will run stable within 10 feet of the house, and at much higher sens settings too.
Bottom line, if I was without an Explorer and know what I do now, I would simply look for a XS with the latest software version, buy the new lower rod assembly for the EX II and SAVE myself some money AND have a great machine !
Yes the the faster software on the EX II, cosmetic upgrades, lower threshold settings,dual digital, etc. are nice additions but I hunt by SOUND only so they aren't that important to me.
Also keep in mind that the XS and EX II will perform exactly the same when it comes down to raw depth capability and anyone that say's otherwise are only fooling themself.
It all depends on what the individual can afford to spend and thinks is important enough to pay the difference for. In other words, don't think that just because a guy shows up with a new EX II and hunts beside you and your XS that he has some HUGE advantage because he does not ... the only difference that will be seen between the two will be the users knowledge that can get the most out of his detector.
Just my 2 cents worth.
H.H.
Mike