Above $1M monthly the maths almost always points to an interchange-plus contract with a tier-1 acquirer. All eight candidates (Adyen, Worldpay, Checkout.com, NMI, Chase, Elavon, Global Payments, Fiserv) are quote-only. The RFP is the work.
Direct answer
Above $1M monthly, run a three-acquirer RFP minimum against Adyen, one US-bank acquirer (Chase, Elavon, or Global Payments), and one global brand (Worldpay or Checkout.com). Always include Helcim's published margin as the control. Expected outcome: IC+ margin in the 5-15 bps range above interchange, plus a fixed processing fee per transaction in the $0.05-$0.15 range, plus a minimum monthly invoice.
Enterprise RFP must-asks
Margin in basis points above interchange, separately by card-present and card-not-present.
Fixed processing fee per transaction.
Minimum monthly invoice.
PCI non-compliance fee (and what it costs to make it disappear).
Account-updater fee structure.
Chargeback handling fee separate from network fee.