Alright so I used Wowheads comparison tool to compare the stats in various set ups with belt/boots comp to be exp capped:
Item Comparison Tool - World of Warcraft
I took for granted that you would want 2x slayer's gear for the 2 tier bonus.
To the left we have Don Alejandro and Slayer's Boots with 2x Delicate Crimson Spinel (10 agi each) cause one of the sockets will have to be a Precise Cardinal Ruby (20 exp, 1,58%), I couldn't include them in the comparison cause they didn't scale properly, which will put you at 3,48% exp.
In the middle we have Shadowmaster's Boots and Slayer's Belt and only 1 Delicate Crimson Spinal, cause you'll have to fill 2 sockets with exp gems which will put you at 3,08 exp.
To the left we have Belt of One Hundred Dreams and Slayer's Boots, with 3x Delicate Crimson Spinel cause you'll be exp capped solely from gear (3,88%).
Ofc I havn't included belt buckles but it shouldn't matter since it would just add an extra socket to each of the comps.
Now choose for yourself how you would want to cap exp, and if you even want to.
For me the exp form Slayer's Boots seems rather crucial considering you already want 2 pieces of Slayer's for the 2 tier bonus. And I'd say the first comp is the best: 10 agi, 9 stam, 19 crit > 19 agi > 33 haste, 1 crit, 2 hit