I'm in kind of the same situation. I just picked up a sizeable account (4 acres weekly, with an additional 3 acres biweekly). It will be a strain to get it done with the equipment I have in the time I have available.
I would like to purchase a 60" Lazer or DC, but would have to finance a good portion of the purchase price. If I buy it, it should save me a good deal of time on this account and a few others. That would give me the opportunity to take on more accounts. If it costs me $250 to $300, it doesn't take too much new work to pay for it.
On the other hand, I really don't want to borrow another 8 or 10,000.
I'll see how things go the first week and then decide, but I'll probably go for the new machine so that I have the capability to take on new work.