They are clearly tied in spam department as shown in the VN while UBW is activated. however Gil could outlast shirou if he wants and wait for the UBW to disable.
If Gil uses Ea however we all know the outcome of that.
Wouldn't be much different from their battle in UBW route, so long as Gil is in character. Shirou's weapon spam is an effective counter to Gil's GoB and Shirou's spam would be much quicker to trigger while in UBW. Not to mention that with whatever Noble Phantasms he has in his physical possession, Shirou gains the attributes and knowledge to wield them as efficiently as their original owners while Gil isn't as efficient with the use of such weapons in his treasury, unless he's using Ea and Enkidu. Shirou would have to kill Gil off quickly though as the King of Heroes can outlast him thanks to greater mana reserves and if Gil resorts to Ea, then Shirou is screwed.
If this were a more serious Gil, then Shirou wouldn't last too long as Gil's high knowledge of magic and ability to think of strategies in heated situations would allow him to devise a quick means of dispatching Shirou.