I've been to a number of LE ammo mfg sponsored gel shoots, and also pseudo-scientifically ruptured more than my fair share of milk jugs. A couple of relevant points that might help you out:
*typical police pistol hollow point loads will penetrate about 14"-16" in bare gel, give or take. They also typically seem to stop in 3, sometimes 4 milk jugs very consistently. Since numerous sources will tell you that full expansion is almost immediate (first few inches), we can reasonably expect that X depth in gel will roughly equate to Y depth in water. Obviously, with jugs, you can only really measure in 8" increments, but figure the dual layer of plastic at the juncture between two of them is a reasonable approximation of hide or clothing on the exit side. Probably not much difference in resistance than a spindly little deer rib.
*I consider a one gallon milk jug to be the rough equivalent of about 4-5 inches of gel. If you're playing with hollowpoints, a 4 to 5 jugger would probably make for a DANDY deer load.
* I've gotten nine jugs out of hard alloy LFN/WFN format bullets in both .45 Auto/230gr/830fps and .32/130gr/1250fps. In the case of the .32, changing the alloy to 20-1 but leaving the load alone created a nice mushroom that stopped in 4 jugs.
*Also got 4 jugs and a nice mushroom from a 20-1 .40WFN/180gr/1350fps.
*Have fired a hard alloy Lyman 358430 (195gr round nose) into FBI gel at 570 fps to see what the old British Webley concept was all about. I ran out of gel at 18" and recovered the bullet off the hard rubber backstop.
*clearly from the above, expansion or non-expansion will be a major influence to depth.
*With cast hollowpoints, I think your major design criteria are going to be (1.) does the bullet expand and penetrate adequately at the distance you expect the impact to occur?, and (2.) does your bullet/alloy/impact velocity combination allow your HP cavity to stay together, or does it fragment off? You might need to download to simulate your impact distance.
*My own two cents: a large meplat slug that does NOT expand, or expands minimally, delivered to the right place is going to be a VERY consistent performer, regardless of impact speed, and expansion can be a variable can of worms. Deer taking a solid pass-through cardiovascular hit that does not also take out a supporting bone structure seem to consistently take about 10 seconds to fall over regardless of what you hit them with. If it sounds like I'm saying "save yourself the trouble with the gel", maybe I am just a little bit. Such experiments are fun for their own sake and worthwhile for the knowledge gained, but fact is we're learning in LE circles that energy transfer isn't really a useful thing; hyrdostatic shock doesn't really start helping us until we've got impact speeds of over 2,000 fps; shot placement and initiating rapid blood loss is what it's really all about; and the main "advantage" of expansion is that it chills out those who are more concerned about "over-penetration" in an urban setting than they are about stopping the threat. A solid flat nose will drop your deer just fine and be easier to cast.