The best replacement for 512 is 552.

The best alternatives to 512 are rated as following:
★★★★★  552
★★★★  256 ssd
★★★  xps2
★★  1gb ram
★★  1gb graphics card
★★  4k sectors
★★  517 eotech
★★  4839
★  517
★  256 video card
★  1 gb
★  912
★  552 eotech
★  602
★  1024
★  watson 749
★  aimpoint pro
★  4k sector size
★  m357
★  1gb graphics
★  512e
★  221
★  testarossa
  1mb cache
  1 gig
  516
  256
  whirlpool
  bp 511
  winpe
  749
  522
  553

Your alternative for 512 is not listed? Suggest!
Speaking about 512, one probably shouldn't forget about magnifier.

Other search terms related to 512 and their ratings are:
★★★★★ magnifier
★★ g33
★ vortex magnifier
★ primary arms magnifier
magpul mbus
256
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Google Trends

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512
552
256 ssd