A new bugfix release of steem (0.20.6) is currently prepared for release next week. Hive account@reggaemuffin already merged the most important changes into his live test environment https://testbed.reggaemuffin.me/ (more infos.

I will do some tests regarding the changed RC costs:
The broadcasted operation can be seen https://steemd.com/@beembot

RC costs measurements

Version 0.20.5 was measured on https://api.steemit.com. 0.20.6 was measured on https://testbed.reggaemuffin.me/.

The RC costs were measured by:
For 0.20.6 (https://testbed.reggaemuffin.me/)

        node = "https://testbed.reggaemuffin.me/"
        stm = Steem(node=node, keys=[wif_posting])
        account = Account("beembot", steem_instance=stm)        
        rc_mana_old = account.get_rc_manabar()
        print(account.steem)
        # place for broadcast a operation      
        sleep(5)
        rc_mana_new = account.get_rc_manabar()
        rc_costs = rc_mana_old["current_mana"] - rc_mana_new["current_mana"]
        print("RC costs: %f G RC" % (rc_costs / 1e9))

For 0.20.5 (https://api.steemit.com):

        stm2 = Steem(node = "https://api.steemit.com", keys=[wif_posting])
        account = Account("beembot", steem_instance=stm2)
        rc_mana_old = account.get_rc_manabar()
        print(account.steem)
        # place for broadcast a operation      
        sleep(5)
        rc_mana_new = account.get_rc_manabar()
        rc_costs  = rc_mana_old["current_mana"] - rc_mana_new["current_mana"]
        print("Costs: %f G RC" % (rc_costs / 1e9))   

Measurements

Transfer

version	RC costs [G RC]
0.20.6	0.300629
0.20.5	0.254544

Vote

version	RC costs [G RC]
0.20.6	0.115230
0.20.5	0.288244

Custom_json (follow)

version	RC costs [G RC]
0.20.6	0.404449
0.20.5	0.070962

Custom_json (reblog)

version	RC costs [G RC]
0.20.6	0.106790
0.20.5	0.092349

Comment

version	RC costs [G RC]
0.20.6	1.966627
0.20.5	1.821318

Conclusion

RC costs for a vote and a follow custom_json operation will be changing. RC costs for a vote are reduced by a factor of 2.5. RC costs for a follow custom_json OP are increased by a factor of 5.6. The RC costs of other custom_json operation is not affected.

The RC costs of all broadcasted operations are slightly increased, as now the execution time is now included in the RC cost calculation.

Link to the commits:

There are three changes related to RC costs:

• execution time: https://github.com/steemit/steem/commit/27b3e5e92682cb3c042e3dd6938eef9e5ef0117c
• Reducing custom_json execution time and increasing custom_json follow execution time: https://github.com/steemit/steem/commit/47ce5099ba254141b4ffe97bb3187d3a21369365
• Reducing RC costs f or a vote: https://github.com/steemit/steem/commit/673c86fa572d54d7d7a982ca8cb7c2440d8eb214