I mean that with PRS-505 , the flashing code never overwrites certain core functionality of the Reader - and that remaining functionality is enough to re-flash the Reader with official firmware. With PRS-700, you overwrite the whole firmware at once. If that fails, there won't be anything left. Thus, no chance for reflash.
Percentage of success - how should I know? I have never even seen a PRS-700! As far as I know, the success rate is 0% (no successful flash) - but the failure rate is 0% as well (no destroyed reader). You should ask users who have a PRS-700, preferably on the-book.org where many people have used the russian hack which is what I use as well.
My hack is pretty much based on the russian hack, so if that one works, my should as well. It's just that due to PRS-700's firmware layout, any fault can easily destroy all of the firmware. On PRS-505, on the other hand, the current hacks only updates one part of a firmware, so even if it gets completely broken, you still have the main code including USB support working and can reflash.
Don't, DON'T try to convert PDF to LRF. I know that viewing PDF files on small-screen readers is awful, but it is still better than converting the PDF to anything else and trying to view that.
Back to the question of fonts: If you want to try out PRS-700 despite the risk of bricking your reader, e-mail me at forum at pepak.net. I will need the fonts you plan to use and, if possible, your current PRS-700 firmware (without it I will need to use the hacked russian firmware as a basis, which would work, but I don't know which changes were put into it). Then I can prepare a hack for you to try. But once again I must warn you: It may irrecoverably brick your reader!
First, you could have created a relevant topic rather than post to an unrelated one.
At the moment I don't have any PRS-700 hacks. I have something that might work, but it hasn't been tested at all and it is missing a rather crucial part - the original PRS-700 firmware. If you can get me an unchanged PRS-700 firmware, I will see about modifying it and then you can test my hack. A word of caution though: It is quite possible to completely and irrevocably brick a PRS-700.
Also, I am not sure about arabic support. It depends on whether the language is closer to european languages or east-asian - the eastern languages are very problematic due to the huge font size.