Simmons is arguably the best athlete in draft next to Becton and Wirfs but a guy I like that can be had in either 3rd or 4th round is Troy Dye. Dye was injured late in season (meniscus) so he couldn't participate at Combine or workouts but he is a 3 down LB who can cover like Simmons and can tackle. He and Simmons have nearly identical measurements (both 6'4 around 230 LBs). I think Simmons is off the board at #8 but if he is there with Wirfs or Okudah I would take either of them before Simmons.
Here is your defensive freaks list for dudes after round 1...
Davion Taylor - LB - Colorado
6'0 228. Late to football guy who needs to refine his game. Serious athlete 4.4 40 and great broad and vert.
Willie Gay JR - LB - Mississippi St.
6'1 243. Explosive athlete. Missed games due to NCAA issues.
Cameron Brown - LB - Penn St.
6'5 233. Didn't run the 40 as fast as I thought he would, but showed burst and athleticism on film.
Troy Dye - LB - Oregon
6'3 231. Three down LB who runs in a conference that is wide open. Never comes off the field. The question is can he hold up physically as a LB as the Pac 12 is pretty finesse.
DJ Wonnum - EDGE - South Carolina
6'5 258. Ran a 4.73 but was also top 20 in most athletic testing in the tough front 7 group.
Azur Kamara - EDGE - Kansas
6'3 245. Another late to football kid. Ran a 4.59 and tested well across the board. Raw player.
Derrek Tuszka - EDGE - North Dakota St.
6'4 251. Sub par competition but made plays. Would need to transition to OLB. Above average athlete.
Kyle Dugger - S/LB - Lenoir-Rhyne
6'1 217. Ran sub 4.5 and tested in the top 7 of all DBs in broad and vert. Great athlete with a history of dominating bad competition. Will need work but seems to be a grinder.
Jeremy Chinn - S/LB - Southern Illinois
6'3 221. Ran 4.45. Similar to Dugger that he was in the top 7 of all DBs in broad and vert. Another great athelet vs marginal competition. Was used similar to Isaiah Simmons being all over the field.
L'Jarius Sneed - S/CB - Louisiana Tech
6'0 192. Ran a 4.37. Don't know if he sticks at S as he has rare length and speed for a CB. Work in progress.