The biggest issue is the where the invisibility is for sure, but you knew that. The frame rate also drops from the sniper perch while using the sniper. I was just checking the map out in a custom game by myself (not forge) and I still had framerate issues. The best way to determine framerate issues IMO is to use the sniper rifle. It tends to create more lag than any other weapon. I was able to remove the lag from the sniper perch by turning the 1x1 blocks around and removing the "torches". Maybe just turning them around would fix it, but I didnt try just that. The reason for that is the pieces with the most reflection cause the most framerate issues. From the Invisibility you are going to have more issues getting rid of the framerate issue. I beleive that most of the lag is coming from the distant scenery. I tried blocking the scenery with two colosseum walls. that took away a lot of the lag but not all of it. I would also try to remove as many reflective items viewable from that point... which is basically that entire corner. Please do not think that I am in anyway bashing your map because it really is an amazing remake and way closer than anyone has come. I do think that in order to make it playable, you may have to remove some of the polish.
This is a really nice remake in terms of aesthetics, but probably the 2 most critical jumps are super hard (bottom blue to top gold and center platform to S3). Smoothing those is critical to retaining the quality of gameplay.
Well, as I've stated previously, the new Reach jump physics do not allow for all the jumps to work exactly the same way as in Halo 3. The jump from mid to sniper can be made from the 1x1 block up, but not from the railing. The lower to mid can be made from the ramp, just not from the bottom 2x2 block. If I raised the 2x2 any, the depths would be off to much and Elites would not make the headroom into sniper hall. With remakes you have to have a little given and take with the different physics between Reach and Halo 3.