$540 via promo credit when you add a new smartphone line with your own 4G/5G smartphone on postpaid Unlimited Plus plan between 5/18/23 - 5/31/23 & port-in req'd. Promo credit applied over 36 months; promo credits end if eligibility requirements are no longer met.
There should be no need to optimize the Mac. The TCP/IP stack on OS X (ultimately BSD/FreeBSD-based) is robust enough to handle most modern connections without issue, especially anything on DSL. FiOS is another story however...
But in case you still wish to run it, use this if you have FiOS: http://support.apple.com/downloads/Broadband_Tuner_1_0
I would not bother on DSL though.